Low pass filter



Feb. 5, 1963 Filed NOV. 1, 1960 R. S. DAVIDSON, JR

LOW PASS FILTER 2 Sheets-Sheet 1 Feb. 5, 1963 R. s. DAVIDSON, JR3,076,947

LOW PASS FILTER 2 Sheets-Sheet 2 Filed Nov. 1, 1960 im., MW W., WW f w WN. m w J c 4 M M @d United States Patent Office l 3,6763@ LDW PASSFHLTER Richard S. Davidson, fr., Redondo Beach, Calif., assigner toHughes Aircraft Company, Cuiver City, Calif., a

corporation of Betan/are Filed Nov. l, 1964i, Ser. lslota 66,536 3Claims. (Cl. 333-9) This invention relates to filters and particularlyto a miniature low pass filter that has a relatively low cutofffrequency and provides a relatively large and consistent attenuationover a wide frequency range.

One arrangement to accomplish low pass filtering is with a standard 1rsection filter. However, a conventional 1r section involves separateinductive and capacitive components with interconnecting wiring whichincreases the sizc of the filter package. Another factor contributing tothe requirement of large filter packages is the conventional use oftoroid shaped cores in the inductor. Also, the interconnecting wiringmay contribute reactive characteristics which causes the lter to providea relatively small attenuation of signals at high frequencies.Undesirable distributed capacitance is inherently developed in theinductive coil so that a relatively low impedance is presented to highfrequency components of the filtered signal. Also, series inductance isinherently developed in the wiring connecting the capacitance elementsto a reference potential so that the attenuation charactistics arelimited at higher frequencies above the pass band.

The volume and weight of lter units are major factors in such equipmentas compact computer units or aircraft flight control systems. This isparticularly true in connection with low pass lter units requiring arelatively low cutoff frequency and improved attenuation characteristicsin response to high frequency signals which conventionally have beenprovided with relatively large volume and weight.

lt is thus an object of this invention to provide an improved miniaturelow pass filter requiring a greatly reduced volume while maintainingperformance characteristics.

it is a further object of this invention to provide an improved compactand easily mounted low pass filter having relatively large capacitanceand inductance values with the filter having minimum overall dimensions.

It is a still further object of this invention to provide an improved,easily constructed low pass filter which exhibits a relatively largeuniform insertion loss over a wide range of frequencies above the passband.

Briefly, in accordance with this invention, two disc type capacitors andan inductor are mounted in a hollow cylindrical cause to form annetwork. The disc capacitors each have a first plate attached directlyto the case with the second plates attached to terminals in afeedthrough arrangement. By attaching the first plates directly to thecase, a maximum capacitance is provided with a minimum of undesiredseries inductance between the capacitor and the case. Mounted betweenthe capacitors are two cylindrical shaped ferromagnetic cores having anannular groove therein. An inductor coil arranged to minimizedistributed capacitance is disposed in the annular groove andelectrically coupled between the second plates of the capacitors.Because of the selection and arrangement of elements, the filter has aminimum of dimensions, provides a low cutoff frequency and providesimproved insertion loss characteristics.

The novel features of this invention, as well as the invention itself,both as to its organization and method of operation, will best beunderstood from the accompanying description taken in connection withthe accompanying drawings in which like characters refer to like partsand in which:

Patented Fels. 5, i953 PIG. l is an external view of the highly compactlow pass filter in accordance with this invention;

FIG. 2 is a sectional side view showing the construction of the low passfilter of FIG. l;

FIG. 3 is a perspective drawing showing in greater detail the inductorportion of the filter of FiGS. l and 2;

FIG. 4 is a schematic diagram of the 1r section formed by the filter ofFIGS. l and 2; and

FIG. 5 is a graph of frequency versus insertion loss for expiaining theimproved operating characteristics of the filter of FIGS. l and 2.

Referring to the external view sectional View of FiG. 2, the tubularmounting case i@ having an annular inner surface i2 centered on alongitudinal axis i4. Externally the mounting case l@ has a hexagonalflange f6 extending radially outward from the body of the tubular caseli) and has one end threaded as at iii and the other end having a smoothsurface as at 22. it is to be noted that other external arrangements ofthe case it) may be utilized in accordance with this invention. The caseiii may be of brass material plated with silver or gold so as to providea reliable ground connection to equipment structure (not shown). t oneaxial end of the case itl a rst capacitor 23 is provided with an annularplate 26 of a conductive material and having a centrally disposedannular opening 27, an annular plate 23 of a dieiectric material andhaving a centrally disposed annular opening 29 and an annular plate 3i)having a centrally disposed annular opening 31. The external diameter ofthe plate 2d is slightly less than the internal diameter of the surface12 so as to be easily assembled and attached or sweated thereto such asby an annular ring of solder 32 which provides direct connection to thecase if?. The annular plate Sil has an external diameter substantiallyless than that of the surface 1 2 so as to be electrically isolatedtherefrom. The external diameter of the plate 2S is the same as that ofplate 2e, and the thickness of the plate 2S along the axis i4 isdetermined by the required voltage capability. The plates 26 and 3i) maybe of a suitable conductive material such as silver being vacuumdeposited on the dielectric plate 28. A suitable dielectric materialsuch as a ceramic type material having a high dielectric constant may beutilized for the plate 2S.

Projecting through the annular openings of the plates 26, 23 and 30 in afeedthrough arrangement is a first connecting terminal 36 which may havea central portion 38 of a first diameter increasing at one end as shownat 4o and being flattened at the other end to a strip at 42 which mayinclude a semicircular notch 37 for ease of providing an electricalconnection. The surface at 4i) is electrically connected to the plate 3dsuch as by an annular solder ring Lid.

A first core 5f) of an inductor 51 is provided, being formed from acylindrical body with a fiat surface 53 at one axial end and an annulargroove 52 at the other axial end to form an external ring 54 and acentral post or projection 53. As may be seen in FIG. 3 a narrow openingor slot S9 is provided in the core Sti extending from the annular groove52 through the external ring 54. Also a similar second core ed isprovided, being formed from a cylindrical body with a flat surface 6i atone axial end and an annuiar groove 62 at the other axial end to form anexternal ring 66 and a central post or projection 68. A slot 69 (FIG. 3)is provided in 'the core 6i) extending from the annular groove 62thro-ugh the external ring 66 for a small distance around thecircumference thereof. The first core Sti has the flat surface 53disposed adjacent to the end liti of the first terminal 36 separatedtherefrom by a thin film of potting material of an annular ring 79 andhas the central post 58 adjacent and concentric to the of FIG. l and tothe low pass filter includes a post 68 of the second core dii butseparated by a space '72.

The space 72 may include a potting material having a permeability nsubstantially similar to that of air so as to provide a desired overallpermeability to the core material with a selected saturation value. Thesurfaces 58 and 68 are maintained with the desired separation distancea'a by a spacing ring 76 which may be of a Teon material, for example,also having dielectric constant similar to air. The annular mass ofpotting material '79 protects the capacitor 23 and core 50 from forcesapplied to the end 42 of the iirst terminal 36. The cores 50 and 60 arethus centered on the axis 14 and intermediate between the tw-o axialends of the case 10. An electrical insulating tape 80 is disposed aroundthe cores 50 and 60 so as to provide electrical isolation of theinductor 31 from the case 10.

At the axial end of the case r opposite to the capacitor 23, a capacitor84 which is similar to the capacitor 23 is provided with an annularplate 86 of a conductive material having a centrally disposed annularopening 88, an annular plate 90 of a dielectric material having acentrally disposed annular opening 92 and an annular plate 96 having acentrally disposed annular opening 94. The plate 86 is adjacent to theexternal flat surface of the plate 90 and the plate 96' is adjacent tothe inward surface along the axis 14 of the plate 90, the plates 86 and96 being, for example, deposited silver similar to the plates of thecapacitor 23. The external diameter of the plate 86 is slightly lessthan the internal diameter of the surface 12 so as to be easilyassembled and attached or sweated thereto such as by an annular ring ofsolder 98. The annular plate 90 has substantially the same externaldiameter as the annular plate 86 and the annular plate 96. has anexternal diameter substantially less than the internal diameter of thesurface 12 so as to be electrically isolated therefrom. Similar to thecapacitor 23, the axial thickness of the plate 90 is determined by there-y quired voltage capability of the capacitor.

' Projecting through the annular openings 88, 92 and 94 of the capacitor84 in a feedthrough arrangement is a second terminal 102 which may havea central portion 104 and an enlarged end 108 having an expanded conicalshape. The other end of the terminal 102 may be flattened to a strip at112 with a circular notch 114 for ease of providing an electricalconnection thereto. The end 108 of the terminal 102 is electricallyconnected to the annular plate 96 such as by an annular ring of solder118. The annular surface at the end 10-8 of the terminal 102 is disposedadjacent to the surface 6 1 of the core 6.0 being separated therefrom bya thin layer. of potting material. An annular mass 120 is disposedaround the annular ring of solder 118 to protect the capacitor 84 fromforces applied to the external portion 112 of the termina] 102.

Referring now also` to FIG. 3 a coil 124 is disposed within the annulargrooves 52 and 62 of the cores 50 and 60 to provide the inductor 51 ofthensection in accordance with this invention. The coil 124 may have aninternal winding or layer 128 with one end 130 of the coil 124 passingthrough the slot 59 to encircle a portion of the enlargedend 40 of theterminal 3,6. The end 130 is electrically connected to the terminal 36as well as .to the plate 30 by the annular ring of solder 46.

"The wire of layer 128 continues from the layer 128 through anintermediate layer 134 to an external layer 136 and to van end 138 whichis passed through the slot 69 and partially wrapped aroundthe enlargedend 108 of the terminal 102. The end 138 is electrically connected tothe terminal 102 as well as to the plate 96 by the annular ring ofsolder 118. The coil 124 has an odd number of layers so as to minimizestray capacitance across the 1r section inductance. It is to be notedthat the coil 124 may have any desired number of layers preferably anodd number for ydeveloping a minimum distributed or stray capacitance.The wire of the 4coil 124 may be insulated by avarnish coating but and60 by a separate structure as in conventional mis not isolated from-thecores 50Y ductors. The insulating tape 80 provides electrical isolationof the inductor 51 from the case 10 where the varnish coating isaccidentally broken or removed adjacent to the cores 50 and 60. Byutilizing the insulation tape 50 to isolate the inductor S1, a largercoil 124 may be disposed in the annular slots 52 and 62.

In order to seal the filter from external moisture, annular masses 142and 144 of a suitable potting material such as epoxy is disposed at therst and second axial ends of the case 10 around the respective terminals36y and 102.

Now that the assembled arrangement of the miniature`- 1r section lterhas been explained in accordance with this invention, the assemblyprocedure thereof will be discussed. For assembling they inductor 51 thecoils 50 and 60 with a small quantity of adhesive film placed on theends of the posts 58 and 68 are firmly and concentrically forcedtogether against the ring spacer 76 with the coil 124 positioned in theannular grooves 52 and 62 and with the coil ends 130 and 138 extendingthrough the respective slots 59 and 69. When suicient pressure isapplied to the cores 50 land 60 so that the spacer 76 is firmly clampedtherebetween, the assembled inductor 51 of FIG. 3y is cured. Forexample, when the adhesive in the space '72 is epoxylite No. 6203, theinductor 51 is cured for approximately two hours at 200 F. After thiscuring operation isv completed, two to four turns of electrical tapesuch as Scotch No. 56 are applied around the cores 50 and 60 to form theinsulating strip 80. The insulating strip 80 extends axially beyond thesurfaces 51 and 61 to insure that the ends 130 and 138 of the coil 124are electrically isolated from the case 10. The next step in theassembly is to form the capacitors 23 and 84 such a's by depositingsilver through screens onto the dielectric plates 28 and 90 and toinsert the respective terminals 36 and 102 through the central axialopenings thereof. The

. capacitors 23 and 84 are then brought into position adjacent to theinductor 51 and respectively soldered to the coil ends 130 and 138 withthe annular solder rings 46 and 118. It is to be noted that preferablythe leads 130 and 138 are wound around the respective terminals 36 and102 at least 270 angular degrees to provide the most desirableelectrical connection. The next step in the assembly is to apply theannular masses of potting material 79 and 120 around the solder rings 46and 118. The capacitors 23 and 84 are then moved into the positionconcentric with the cores 50 and 60 by bending the ends and 138 of thecoil 124 so that the mass of potting material 79 and 120 is abutting thesurfaces S3 and 61 of the cores 50 and 60 and forming a thin layer atthe ends 40 and 108 of the terminals 36 and 102. This subassembly isthen firmly clamped in position while being again cured similar tothatas discussed above. The final step in the assembly of the lter is toinsert the subassernbly including the cores 50 and 60 into positionwithin ca se 1:0 and respectively soldering the external edge Y 0f theannular plates 26 and 86 of the capacitors 23 and 84 to the internalsurface 12 by annular solder rings 32 and 98. The annular masses ofpotting material 142 and 144 are then caused to ow'into the two axialends of the case 10 with the linal assembly filter being again cured asdiscussed above to provide the completed filter of FIGS. 1 and 2.'

Referring now to the 1r section low pass filter circuit of FIG. 4 and tothe insertion loss versus frequency curve of FIG. 5 as well as to FIG.2, an input lead 148 which may be representative ofthe first terminal 36is coupled to one end of the inductor 51 representative of theinductance developed by the coil 124 and the cores 50 and 60. The lead148 is'also coupled through a lead 152 to the plate 30 of the capacitor23 which lead represents the annular solder ring46. The plate 26 iscoupled to ground, that is, to the v,case 10 through a lead '154 whichcoupling represents the annular solder ring 32 in FIG, 2. Ascriesinductance 158 is shown dotted in the lead 154 which represents theconventional selt` inductance of a wire lead but, because of the directconnection of the annular solder ring 32, has a relatively small valuein the lter in accordance with this invention. The other end of theinductor l is coupled to an output lead lez which may represent thesecond terminal 19.2. The second end of the inductor 5l is coupledthrough a lead lod to the plate 96 of the capacitor Se which leadrepresents the annular solder ring lid. The plate Se is coupled througha lead ltl to ground representative or" the annular solder ring 93 tothe case lil. A series inductor 172 is shown dotted in the lead 17d torepresent the conventional self or mutual inductance developed in a wirebut which is greatly minimized by the direct connection of the solderring hd. Coupled across the inductor 5l is a capacitor 174 shown dottedto indicate the distributed capacitance developed across the coil 12d,which may be greatly minimized in accordance with this invention byutilizing the coil 12d with an odd number of layers.

A curve lo of FG. 5 shows the operating characteristics of the filter inaccordance with this invention for L=l270 microhenries for inductor 5l,C=1l,200 micromicrofarads for capacitors 23 and till and having a 50milliarnpere DC. (direct current) capability. For this tiiter with arelatively low DC. capability the spacing ring '75 is not utilized andthe distance dd is essentially zero. The insertion loss is proportionalto the voltage amplitude developed across a selected load in a testcircuit without the filter to the voltage amplitude developed across theload with the filter in the test circuit. The curve la rises from acutoff frequency fc with a steep slope of approxdmately 20 decibels peroctave to a iirst resonant point lli: having an insertion loss amplitudewhich is determined by the frequency of parallel resonance of theinductor 5l and distributed capacitance E17-si. Ey providing an oddnumber of windings to the core "lf-rd so that the ends lita and i3d areat opposite ends of the coil 22d to provide a minimum value to the straycapacitance ll, the resonant point i534 ri es to a relatively highfrequency with a relatively high insertion loss. As is well known, asubstantially large portion of the stray or distributed capacitance in acoil may be developed between the input and output leads. Also, byreducing the distributed capacitance 174 which is essentially a shortcircuit at high frequencies, the insertion loss curve No is maintainedat a relatively high value of insertion loss at high frequencies to theright of point ld. Thus, the low value of the distributed capacitance17d provides the filter with improved attenuation characteristics.

The cutol frequency fc is relatively low because of the relatively largevalues of capacitance and inductance obtained with minimum physicaldimensions. The feedthrough arrangement of the capacitors 23 and 84provides maximum surface area with the case lil having minimumdimensions. The shape of the cores Sil and 6d with the annular slotstherein provides a maximum volume of material and thus contributes to ahigh inductance in a small space. Also, the cores 50 and 60 are selectedof a material having a high permeability ,u to increase the inductance.Further, the utilization of the coil i241; without a conventional bobbinin the annular grooves 52 and 62 as a result of providing isolation atthe insulating tape 80 allows more windings to be utilized in a fixedspace to increase the value of the inductance without increasing theoverall dimensions of the filter. It is to be noted that by utilizingall of the space in the annular grooves 52 and 62 larger wires may beprovided in the coil 124 for a large D.C. current rating.

A second resonant point lilo is present on the curve 17d as a result orthe series resonance of the capacitor 23 and series inductance 153 andof the capacitor S4 and series inductance 72. Because the value of theseries inductance 153 and 172 is greatly reduced in the low pass filterin accordance with this invention by directly connecting the plates 26and 96 to the case 10 by the annular solder rings 32. and 98, the secondresonant point lilo occurs at a relatively high frequency. Thus, arelatively large attenuation is maintained from the frequency at pointld to the very high frequencies. Thus, for example, the curve E76provides a minimum attenuation of 40 decibels (db) between 0.6 mc. andgreater than 1000 mc.

Another advantage of the filter of FIG. 2 is that the air space 72effectively controls the saturation point of the cores 5i) and 69 and byincreasing the distance da provides a high DC. current rating for arelatively small core. However, low frequency attenuation is sacriced tosome extent by increasing the distance da of the gap '72. By varying thethickness da of the spacing ring '76, a desired D.C. current rating maybe obtained without changing the external dimensions of the filter. Thecoil 121i may be of a wire size, for example, to operate over a range orcurrent from 50 milliamperes to 1 ampere so as to standardizeconstruction thereof.

As an example, iilters will be considered 1n accordance with thisinvention having an internal diameter of the surface i2 of 039i inch andan axial length of the case lil of 0.50 inch (overall dimensionsexcluding the terminals of approximately 1/2 inch by 1/2 inch). Withthese dimensions, filters having a 50 milliampere DC. rating and a lampere DC. rating have been developed. rEhe cores 5l) are l: rroxcubeNo. 3323133 of Ferroxcube 3C material having a relatively largepermeability u. The coil 24 was constructed of No. 28 varnished wire ofthree layers as shown in FGS. 2 and 3. Other elements were constructedof materials in accordance with the examples discussed above. The 50milliampere iiltcr has a spacing distance da of essentially zero and thel ampere filter had a distance d2u of .005 inch. The 50 milliamperefilter provided a minimum of l0 decibels insertion loss between afrequency of 0.7 mc. and 1000 rnc. and had a cutoff frequency fc ofapproximately 130 kc. as shown in FlG. 5. The l ampere rated filterprovided a minimum of 40 decibels insertion loss between frequencies of1.5 mc. to C' mc. and had a cutoff frequency fc of 300 kc. Thus, it maybe seen that for a relatively small size and at a relatively large DC.current rating, low cutoff frequencies and a consistently highattenuation to a very hi'rh frequency is obtained with the filter inaccordance with this invention. Another advantage is that the same core12d may be utilized to develop a filter with a relativey low or high DC.current rating by only varying the thickness da of the space 72 andwithout varying the overall dimensions.

lt is to be noted that the miniature filter in accordance with thisinvention is not limited to a particular size or value as discussedabove, but may have many values and s1zes.

rihus, there has been described a miniature low pass radio frequencyfilter which provides a low cutoff frequency by an improved inductancearrangement of a coil and cores. Because of the improved arrangement ofthe capacitors, a high insertion loss is maintained to a very highfrequency range.

What is claimed is:

l. A low pass 1r section filter comprising a cylindrical case of aconductive material for being coupled to a source of referencepotential, first and second annular plates of a conductive material eachhaving a centrally located annular opening and peripherally electricallyconnected to opposite axial ends of said cylindrical case, third andfourth annular plates of dielectric material having a centrally locatedannular opening and respectively disposed adjacent to and axially inwardfrom said first and second plates, lifth and sixth annular plates of aconductive material having a centrally located annular opening anddisposed respectively adjacent to and inward from said third and fourthplates, the periphery of said fifth and sixth plates being electricallyisolated from said case, rst and and second axial end vand having anannular groove extending inward from said first end to form 'an outerringy and an axial projection, said first and second cores being axiallydisposed between said fifth and sixth plates with the outer rings andaxial projection adjacent to each other, first and second terminal meansrespectively projecting through the annular openings in said first andthird and in said second and fourth plates and electrically connected tosaid respective fifth and sixth plates, a continuously wound coil havingan odd number of layers of windings disposed inthe annular groove ofsaid first and second cores and coupled between said fth and sixthplates, and electrical insulating means disposed between thecircumferential external surface of said first and second cores and saidcylindrical case. t

2. A low pass 1r section filter comprising a tubular mounting casehaving a longituidnai axis and an annular axial opening, first andsecond annular plate capacitors each having a first and second plate ofa conductive material separated by a third plate of dielectric materiaLsaid capacitors hav-ing a central annular opening, said first and secondcapacitors disposed at opposite axial ends of said case in said annularopening with said first lplates adjacent to the axial ends of said case,respective first and second annular solder rings electrically connectingthe circumferential edges of said first plates to said case, first andsecond cores each having a cylindrical body with a longitudinal axis anda first and second axial end with an annular groove extending axiallyinward from said first end to form an axial center projection thereat,said first and second cores disposed axially in said annular opening insaid case between said first and second capacitors with said first endsadjacent to each other, a coil having an odd number of layers of wiredisposed in said annular openings of said Ifirst and second cores andhaving first and second ends respectively extending to said first andsecond capacitors, and first and second terminals respectively disposedthrough the annular openings in said first and second capacitors andelectrically connected to said respective second plates of said firstand second capacitors, and to said respective Vfirst and second ends ofsaid coil.

3. A 1r section low pass filter comprising a tubular mounting casehaving a longitudinal axis andan annular opening extending along saidaxis, first and second capacitors each including an annular plate of adielectric material having an annular opening at the radial centerthereof and first and second annular plates having an annular opening atthe radial center thereof of a con-A ductive material and attachedconcentrically to opposite flat sides of said annular plate ofdielectric material, said first and second capacitors being disposed atrespective first and second axial ends of said case, with said firstplates of said first and second capacitors respectively facing the firstand second ends and said first plates being electrically connectedaround the circumference thereof to sai-d case, first and second coreseach having a cylindrical body with a first and second end with anannular groove extending axially inward from said first axial end, saidfirst and second cores being disposed substantially axially in saidtubular case with the annular grooves of said first axial end beingadjacent, each of said cores having a slot extending from said annulargroove to said second end thereof, acoil having an odd number of layersof wire disposed within said annular grooves and having first and secondends passing through said slots, annular insulating means disposedaround the external circumference of said first and second cores, firstand second terminals inserted through the annular openings in said firstand second capacitors each having one end respectively adjacent to thesecond axial ends of said first and second cores, electrical connectingmeans connecting the respective first and second ends of said coil thesecond plates of said respective first and second capacitors and theends of said respective first and second terminals, and means enclosingthe axial ends of said tubular case around said first and secondterminals.

References Cited in the file of this patent UNITED STATES PATENTS1,803,868 lPorter a May 5, 1931 2,728,054 Albers-Schoenberg Dec. 20,1,955 2,759,155 Hakenberg Y Aug. 14, 1956 2,948,871 Craig@l s Augt 9,i960 FOREIGN PATENTS 818,775 Great Britain Aug 26, 195,9

OTHER REFERENCES Allen-Bradley Technical Bulletin No. 5410, January 16,1958, 3 pages.

1. A LOW PASS $ SECTION FILTER COMPRISING A CYLINDRICAL CASE OF ACONDUCTIVE MATERIAL FOR BEING COUPLED TO A SOURCE OF REFERENCEPOTENTIAL, FIRST AND SECOND ANNULAR PLATES OF A CONDUCTIVE MATERIAL EACHHAVING A CENTRALLY LOCATED ANNULAR OPENING AND PERIPHERALLY ELECTRICALLYCONNECTED TO OPPOSITE AXIAL ENDS OF SAID CYLINDRICAL CASE, THIRD ANDFOURTH ANNULAR PLATES OF DIELECTRIC MATERIAL HAVING A CENTRALLY LOCATEDANNULAR OPENING AND RESPECTIVELY DISPOSED ADJACENT TO AND AXIALLY INWARDFROM SAID FIRST AND SECOND PLATES, FIFTH AND SIXTH ANNULAR PLATES OF ACONDUCTIVE MATERIAL HAVING A CENTRALLY LOCATED ANNULAR OPENING ANDDISPOSED RESPECTIVELY ADJACENT TO AND INWARD FROM SAID THIRD AND FOURTHPLATES, THE PERIPHERY OF SAID FIFTH AND SIXTH PLATES BEING ELECTRICALLYISOLATED FROM SAID CASE, FIRST AND SECOND CORES EACH BEING A CYLINDRICALBODY HAVING A FIRST AND SECOND AXIAL END AND HAVING AN ANNULAR GROOVEEX-